High-strength and high-toughness fibrous low-carbon alloy steel as well as preparation method and application thereof

Abstract

The invention relates to the technical field of metal materials, and provides high-strength and high-toughness fibrous low-carbon alloy steel as well as a preparation method and application thereof. The high-strength and high-toughness fibrous low-carbon alloy steel provided by the invention comprises the following chemical components: C, Mn, Si, Cr, Mo, Nb + V, Ni, Cu, Al and Fe, and the metallographic structure is a complex-phase fibrous structure of martensite, ferrite and retained austenite. According to the low-carbon alloy steel, the synergistic effect of Mn, Si, Cr and Mo is utilized, Ni, Al, Cu and other alloy elements are added for component modification, and the complex-phase fibrous structure design of martensite, ferrite and retained austenite is combined, so that the low-carbon alloy steel has high strength, high toughness and high deformation strengthening capacity, and an ultrahigh-strength steel wire of 2000 MPa or above is easily obtained through cold drawing. The material can be obtained through simple brine quenching, environmental pollution caused by lead bath isothermal quenching is avoided, the heat treatment cost is reduced, and the material has wide application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of metal materials, and in particular to a high-strength and high-toughness fibrous low-carbon alloy steel, a preparation method thereof, and an application thereof. Background Art

[0002] Since the 21st century, with the construction of megaprojects such as the Hong Kong-Zhuhai-Macao Bridge and the Shenzhen-Zhongshan Link, modern bridges have rapidly developed towards longer spans, lighter weight, and longer lifespans. As the core load-bearing components of bridge structures, the service performance of main cables and stay cables directly determines the safety and economic efficiency of bridges.

[0003] Cable wire rod is the wire used to manufacture cables. It is typically made of alloy steel. The alloy steel used to make cable wire rod must have high strength and toughness to meet service requirements. The industry primarily uses alloying and heat treatment processes to improve the mechanical properties of steel wire. The currently commonly used method is carbon strengthening: the carbon content of the steel wire rod is increased to a range of 0.9-1.0wt%, and then a lead bath austempering process is used to transform the austenite into an ultrafine bainite structure with a lamellar spacing of approximately 30-50nm. This microstructural feature can achieve a breakthrough in the tensile strength of the steel wire. However, when the carbon content exceeds the critical value of 0.9wt%, the elongation of the steel drops sharply to below 5%, and the cross-sectional reduction rate is less than 30%, resulting in frequent brittle fracture of the material during subsequent processing. Summary of the Invention

[0004] In view of this, the present invention provides a high-strength and high-toughness fibrous low-carbon alloy steel and its preparation method and application. The low-carbon alloy steel provided by the present invention has high strength and good toughness and has broad application prospects in bridge cable wire rod materials.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] A high-strength and high-toughness fibrous low-carbon alloy steel comprises the following chemical components by mass fraction: C: 0.1-0.3%, Mn: 2-5%, Si: 0.3-1.5%, Cr: 0.3-1%, Mo: 0.1-0.8%, the total amount of Nb and V ≤ 0.1%, Ni: 0-1.5%, Cu: 0-1.2%, Al: 0-1.5%, and the balance is Fe and unavoidable impurities; the contents of Ni, Al and Cu are not all zero at the same time; the metallographic structure of the high-strength and high-toughness low-carbon fibrous alloy steel is a complex phase fibrous structure of martensite, ferrite and retained austenite.

[0007] Preferably, the high-strength and high-toughness low-carbon alloy steel has a tensile strength of ≥1300 MPa, an elongation of ≥15%, and a hardness of ≥410 HV.

[0008] The present invention also provides a method for preparing the high-strength, high-toughness, low-carbon alloy steel described in the above scheme, comprising the following steps:

[0009] (1) melting the raw materials and then casting to obtain a casting blank;

[0010] (2) cooling the forged billet to obtain a forging;

[0011] (3) austenitizing the forging and then quenching it to obtain an austenitic forging;

[0012] (4) The austenitic forging is subjected to two-phase region cyclic quenching and then tempered to obtain the high-strength and high-toughness fibrous low-carbon alloy steel; the two-phase region cyclic quenching includes cyclic two-phase region heating and quenching; the temperature of the two-phase region heating is 700-840°C; the number of two-phase region cyclic quenching is greater than or equal to 1 time.

[0013] Preferably, the smelting temperature is 1400-1500°C, the casting temperature is 1400-1500°C; the initial forging temperature is 1100-1200°C, and the final forging temperature is 850-950°C; the total deformation rate of the forging is 79-80%.

[0014] Preferably, the temperature of the austenitizing treatment is 890-910° C., and the holding time coefficient is 1.4-1.6 mm / min.

[0015] Preferably, the medium used for quenching in step (3) is brine, and the components of the brine include sodium chloride and water. The mass fraction of sodium chloride in the brine is 4-6%, and the mass fraction of water is 94-96%.

[0016] Preferably, the holding time coefficient of a single heating in the two-phase zone heating is 0.45 to 0.75 mm / min;

[0017] During the process of heating to the temperature of the two-phase region heating, when the temperature is higher than 300° C., the heating rate is controlled at 2° C. / min to 15° C. / min.

[0018] Preferably, in the two-phase region circulating quenching, the quenching medium used is brine, the components of the brine include sodium chloride and water, the mass fraction of sodium chloride in the brine is 4-6%, and the mass fraction of water is 94-96%.

[0019] Preferably, the tempering temperature is 150-200° C., and the tempering time is 50-70 minutes.

[0020] The present invention also provides the use of the high-strength and high-toughness fibrous low-carbon alloy steel described in the above scheme or the high-strength and high-toughness fibrous low-carbon alloy steel prepared by the preparation method described in the above scheme in the field of cable wire rod materials or machinery.

[0021] The present invention provides a high-strength and high-toughness fibrous low-carbon alloy steel, comprising the following chemical components by mass fraction: C: 0.1-0.3%, Mn: 2-5%, Si: 0.3-1.5%, Cr: 0.3-1%, Mo: 0.1-0.8%, the total amount of Nb and V ≤ 0.1%, Ni: 0-1.5%, Cu: 0-1.2%, Al: 0-1.5%, and the balance being Fe and unavoidable impurities; the contents of Ni, Al and Cu are not all 0 at the same time; the metallographic structure of the high-strength and high-toughness low-carbon fibrous alloy steel is a complex phase fibrous structure of martensite, ferrite and retained austenite. The present invention adds an appropriate amount of one or more of the alloying elements Ni, Cu and Al to the traditional duplex low-carbon steel, and utilizes the alloying effect to inhibit the recovery and recrystallization of lath martensite, improve the nucleation rate of reversed austenite in the process of tissue inheritance, and hinder the interface migration of austenite / ferrite through the partitioning process of Mn, Ni and Cu alloying elements, reduce the lateral growth rate, thereby obtaining a multi-phase fibrous microstructure of martensite / ferrite / retained austenite, and enhance the strength and toughness of the material; at the same time, the Ni element forms a stable solid solution in the austenite phase region, and synergistically promotes the dispersion precipitation of (Mo, Ni) C type composite carbides with the Mo element, significantly improving the hardenability and tempering resistance of the material; the addition of the Cu element synergistically improves the mechanical properties of the material with elements such as Nb and V, and the addition of the lightweight element Al inhibits carbides, refines the original austenite grains, improves toughness, and reduces inclusions to further improve the strength and plasticity of the material. In summary, the present invention utilizes the synergistic effect of elements such as Mn, Si, Cr, Mo, and adds alloying elements such as Ni, Al, and Cu for composition modification, and combines the multiphase fibrous structure design of martensite, ferrite and retained austenite to make the low-carbon alloy steel have excellent mechanical properties of high strength and high toughness, and at the same time have high deformation strengthening capacity, and it is easy to obtain ultra-high strength steel wire of more than 2000MPa by cold drawing, which has broad application prospects in cable wire materials.

[0022] The present invention also provides a method for preparing the high-strength, high-toughness, low-carbon alloy steel described in the above scheme. The preparation method provided by the present invention is simple to operate and easy to mass-produce. Furthermore, the quenching method used in the preparation method of the present invention is salt water quenching. The traditional method uses a lead bath medium to continuously volatilize at high temperature (>400°C), resulting in a lead vapor concentration of up to 0.15-0.3 mg / m3 in the working environment. 3 (far exceeding the OSHA regulation of 0.05mg / m 3 limit), while producing lead-containing quenching waste residue, which constitutes serious heavy metal pollution to the soil and groundwater system; the present invention adopts salt water quenching, which has a good working environment, does not produce lead quenching waste residue, is environmentally friendly, and is suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is an SEM image of the high-strength and high-toughness fibrous low-carbon alloy steel prepared in Example 1;

[0024] Figure 2 This is the EBSD image of the high-strength and high-toughness fibrous low-carbon alloy steel prepared in Example 1;

[0025] Figure 3 TEM image of the high-strength and high-toughness fibrous low-carbon alloy steel prepared in Example 1;

[0026] Figure 4 This is an SEM image of the high-strength and high-toughness fibrous low-carbon alloy steel prepared in Example 2;

[0027] Figure 5 This is an SEM image of the high-strength and high-toughness fibrous low-carbon alloy steel prepared in Example 3;

[0028] Figure 6 This is a metallographic image of the high-strength and high-toughness fibrous low-carbon alloy steel prepared in Example 4;

[0029] Figure 7 This is a metallographic image of the high-strength and high-toughness fibrous low-carbon alloy steel prepared in Example 5;

[0030] Figure 8 This is an engineering stress-strain curve of the high-strength and high-toughness fibrous low-carbon alloy steel prepared in Example 1;

[0031] Figure 9 This is an engineering stress-strain curve of the high-strength and high-toughness fibrous low-carbon alloy steel prepared in Example 2;

[0032] Figure 10 This is an engineering stress-strain curve of the high-strength and high-toughness fibrous low-carbon alloy steel prepared in Example 3;

[0033] Figure 11 This is an engineering stress-strain curve of the high-strength and high-toughness fibrous low-carbon alloy steel prepared in Example 4;

[0034] Figure 12 This is an engineering stress-strain curve of the high-strength and high-toughness fibrous low-carbon alloy steel prepared in Example 5;

[0035] Figure 13 This is the engineering stress-strain curve of the high-strength and high-toughness fibrous low-carbon alloy steel prepared in Example 1 after cold drawing. DETAILED DESCRIPTION

[0036] The present invention provides a high-strength and high-toughness fibrous low-carbon alloy steel, comprising the following chemical components by mass fraction: C: 0.1-0.3%, Mn: 2-5%, Si: 0.3-1.5%, Cr: 0.3-1%, Mo: 0.1-0.8%, the total amount of Nb and V ≤ 0.1%, Ni: 0-1.5%, Cu: 0-1.2%, Al: 0-1.5%, and the balance being Fe and unavoidable impurities; the contents of Ni, Al and Cu are not all 0 at the same time; the metallographic structure of the high-strength and high-toughness low-carbon fibrous alloy steel is a complex phase fibrous structure of martensite, ferrite and retained austenite.

[0037] The chemical composition of the high-strength, high-toughness, fibrous low-carbon alloy steel provided by the present invention includes 0.1-0.3% C by mass, specifically 0.15%, 0.17%, 0.18%, 0.2%, or 0.25%. By controlling the C mass fraction within this range, the present invention can control matrix strength and weldability, ensuring structural integrity.

[0038] Calculated by mass fraction, the chemical composition of the high-strength and high-toughness fibrous low-carbon alloy steel provided by the present invention includes Mn: 2-5%, specifically 3%, 3.5%, 4.2% or 4.5%; the present invention controls the mass fraction of Mn within the above range, which can play a role in austenite stabilization and solid solution strengthening.

[0039] The chemical composition of the high-strength, high-toughness fibrous low-carbon alloy steel provided by the present invention includes Si: 0.3-1.5%, specifically 0.5%, 0.88%, 0.93%, 1.02%, or 1.2%. Controlling the Si content within this range can inhibit carbides and improve toughness.

[0040] Calculated by mass fraction, the chemical composition of the high-strength and high-toughness fibrous low-carbon alloy steel provided by the present invention includes Cr: 0.3-1%, specifically 0.5%, 0.71%, 0.8% or 0.9%.

[0041] The chemical composition of the high-strength, high-toughness, fibrous low-carbon alloy steel provided by the present invention includes Mo: 0.1-0.8% by mass, specifically 0.2%, 0.3%, 0.32%, 0.33%, 0.34%, 0.5%, or 0.6%. By adding Cr and Mo, the present invention can synergistically improve the corrosion resistance and hardenability of the alloy steel.

[0042] The high-strength, high-toughness, fibrous low-carbon alloy steel provided by the present invention comprises, by mass, Nb and V (denoted as Nb+V), with the total Nb+V content being ≤ 0.1%, preferably 0.05-0.1%. By controlling the Nb and V contents within the aforementioned ranges, the present invention can refine grains and suppress grain segregation.

[0043] Calculated by mass fraction, the chemical composition of the high-strength and high-toughness fibrous low-carbon alloy steel provided by the present invention includes Ni: 0-1.5%, specifically 0 (i.e., no Ni is added), 0.5%, 0.6%, 0.8%, 1.0%, 1.2% or 1.5%; the present invention controls the Ni content within the above range, which can play a role in refining the grains.

[0044] The chemical composition of the high-strength and high-toughness fibrous low-carbon alloy steel provided by the present invention includes Cu: 0-1.2%, specifically 0 (i.e., no Cu addition), 0.5%, 0.6%, 0.7%, 0.9%, 0.95%, 1%, 1.1% or 1.2% by mass fraction; the present invention controls the Cu content within the above range, which can avoid hot brittleness of the alloy steel and at the same time play a role in refining the grains.

[0045] Calculated by mass fraction, the chemical composition of the high-strength and high-toughness fibrous low-carbon alloy steel provided by the present invention includes Al: 0-1.5%, specifically 0 (i.e., no Al added), 0.5%, 0.6%, 0.8%, 1%, 1.2%, 1.23%, 1.31% or 1.5%; the present invention controls the mass fraction of Al within the above range, which can inhibit carbides, refine grains, improve toughness, and reduce inclusions.

[0046] Calculated by mass fraction, the chemical composition of the high-strength and high-toughness fibrous low-carbon alloy steel provided by the present invention also includes the balance of Fe and unavoidable impurities.

[0047] In the present invention, the high-strength and high-toughness low-carbon alloy steel has a tensile strength of ≥1300 MPa, an elongation of ≥15%, and a hardness of ≥410 HV.

[0048] The present invention also provides a method for preparing the high-strength and high-toughness low-carbon alloy steel, comprising the following steps:

[0049] (1) melting the raw materials and then casting to obtain a casting blank;

[0050] (2) cooling the forged billet to obtain a forging;

[0051] (3) austenitizing the forging and then quenching it to obtain an austenitic forging;

[0052] (4) subjecting the austenitic forging to a two-phase region cyclic quenching treatment and then tempering to obtain the high-strength and high-toughness fibrous low-carbon alloy steel; the two-phase region cyclic quenching includes cyclic two-phase region heating and quenching; the temperature of the two-phase region heating is 700-840°C; the number of two-phase region cyclic quenching is greater than or equal to 1 time.

[0053] The present invention melts the raw materials and then casts them to obtain a cast billet. The present invention has no special requirements for the raw materials, as long as they can be formulated to produce low-carbon alloy steel with the target chemical composition; the melting temperature is preferably 1400-1500°C, and the casting temperature is preferably 1400-1500°C. The present invention has no special requirements for the melting and casting methods, and methods well known to those skilled in the art can be used.

[0054] After obtaining the ingot, the present invention forges and then cools the ingot to obtain a forged part. In the present invention, the initial forging temperature is preferably 1100-1200°C, specifically 1100°C, 1150°C, or 1200°C; the final forging temperature is preferably 850-950°C, specifically 850°C, 900°C, or 950°C; the total deformation rate of the forging is preferably 79-80%, specifically 79.59%; the cooling method is preferably air cooling, and the terminal temperature of the cooling is preferably room temperature.

[0055] After obtaining the forging, the present invention austenitizes the forging and then quenches it to obtain an austenitic forging. In the present invention, the austenitizing temperature is preferably 890-910°C, specifically 900°C, and the holding time coefficient is preferably 1.4-1.6 mm / min, specifically 1.5 mm / min. The medium used for quenching is preferably brine, and the components of the brine preferably include sodium chloride and water. The mass fraction of sodium chloride in the brine is preferably 4-6%, specifically 5%, and the mass fraction of water is preferably 94-96%, specifically 95%. During quenching, the forging is preferably placed vertically in the quenching medium. The temperature of the quenching medium is room temperature, and the quenching time is preferably 0.05-0.1 mm / min.

[0056] After obtaining the austenitic forging, the present invention performs a two-phase region cyclic quenching treatment on the austenitic forging and then tempers it to obtain the high-strength and high-toughness fibrous low-carbon alloy steel. In the present invention, the two-phase region cyclic quenching includes cyclic two-phase region heating and quenching; the temperature of the two-phase region heating is 700-840°C, specifically 720°C, 750°C, 760°C, 780°C, 800°C, 820°C or 840°C; the holding time coefficient of a single heating in the two-phase region heating is preferably 0.45-0.75 mm / min, specifically 0.5 mm / min or 0.6 mm / min; in the two-phase region cyclic quenching, in the process of heating to the temperature of the two-phase region heating, when the temperature is higher than 300°C, the heating rate is preferably controlled at 2°C / min-15°C / min, specifically 3°C / min, 5°C / min, 8°C / min, 10°C / min or 12°C / min; the present invention has no special requirements for the heating rate when the temperature is below 300°C, and any heating rate can be used. In the two-phase cyclic quenching, the quenching medium is preferably salt water, which preferably includes sodium chloride and water. The mass fraction of sodium chloride in the salt water is preferably 4-6%, specifically 5%, and the mass fraction of water is preferably 91-96%, specifically 95%. The temperature of the quenching medium is room temperature, and the quenching time is preferably 0.05-0.1 mm / min. The number of two-phase cyclic quenching times is greater than or equal to one, preferably 1-3 times. After the two-phase cyclic quenching treatment, a multiphase fibrous structure of martensite, ferrite, and retained austenite is obtained.

[0057] In the present invention, the tempering temperature is preferably 150-200°C, specifically 150°C, 160°C, 180°C, or 190°C; the tempering time is preferably 50-70 minutes, more preferably 60 minutes; and after tempering, the resulting low-carbon alloy steel is naturally cooled to room temperature. Tempering stabilizes the microstructure and homogenizes the microstructure, thereby adjusting mechanical properties such as tensile strength.

[0058] The present invention also provides the use of the high-strength and high-toughness fibrous low-carbon alloy steel described in the above scheme or the high-strength and high-toughness fibrous low-carbon alloy steel prepared by the preparation method described in the above scheme in the field of cable wire rod materials or machinery.

[0059] In the present invention, the cable wire rod material is preferably a bridge cable wire rod material; the mechanical field preferably includes the automotive field or the heavy machinery field; when applied to the automotive field, it is preferably used in automotive lightweight or automotive stamping panels.

[0060] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0061] Example 1

[0062] The chemical composition of the high-strength and high-toughness fibrous low-carbon alloy steel in this embodiment is: C: 0.17%, Mn: 3.5%, Si: 1.02%, Cr: 0.71%, Mo: 0.34%, Nb+V≤0.1%, Ni: 1.0%, Cu: 1.0%, and the remainder is Fe and unavoidable impurities.

[0063] The preparation method is as follows: the raw materials are melted and cast to obtain a billet with a size of 98 mm; the billet is heated to 1150°C and then forged in multiple passes, with a total deformation rate of 79.59% and a final forging temperature of 850°C. After forging is completed, it is slowly cooled to room temperature to obtain a forging.

[0064] The forging is austenitized in a 900°C vacuum tube furnace at a holding rate of 1.5 mm / min, and then vertically placed in a quenching medium for quenching, wherein the quenching medium is salt water containing 5 wt% sodium chloride and 95 wt% water, the temperature of the quenching medium is at room temperature, and the quenching time is 0.05 mm / min, to obtain an austenitic forging. The austenitic forging is subjected to two-phase region cyclic quenching, specifically: first, the austenitic forging is placed in a tube furnace, held at 735°C for 0.5 mm / min, and then quenched in salt water (5 wt% sodium chloride and 95 wt% water), when the temperature is higher than 300°C during the heating process, the heating rate is controlled at 12°C / min, the temperature of the quenching medium is at room temperature, and the quenching time is 0.05 mm / min; the two-phase region cyclic quenching is repeated twice; the forging after the two-phase region cyclic quenching is placed in a 200°C box furnace for holding for 1 hour for tempering, and naturally cooled after the tempering is completed to obtain a high-strength and high-toughness fibrous low-carbon alloy steel.

[0065] Example 2

[0066] The chemical composition of the high-strength and high-toughness fibrous low-carbon alloy steel in this embodiment is: C: 0.18%, Mn: 4.2%, Si: 1.02%, Cr: 0.71%, Mo: 0.34%, Nb+V≤0.1%, Cu: 0.7%, Al: 1.1%, and the remainder is Fe and unavoidable impurities.

[0067] The preparation method is as follows: the raw materials are melted and cast to obtain a billet with a size of 98 mm; the billet is heated to 1150°C and then subjected to multi-pass forging with a total deformation rate of 79.59% and a final forging temperature of 850°C. After forging is completed, it is slowly cooled to room temperature to obtain a forging.

[0068] The forging is austenitized in a 900°C vacuum tube furnace at a holding rate of 1.5 mm / min, and then vertically placed in a quenching medium for quenching, wherein the quenching medium is salt water containing 5 wt% sodium chloride and 95 wt% water, the temperature of the quenching medium is at room temperature, and the quenching time is 0.05 mm / min, to obtain an austenitic forging. The austenitic forging is subjected to two-phase region cyclic quenching, specifically: first, the austenitic forging is placed in a tube furnace, held at 800°C for 0.5 mm / min, and then quenched in salt water (5 wt% sodium chloride and 95 wt% water), when the temperature is higher than 300°C during the heating process, the heating rate is controlled at 10°C / min, the temperature of the quenching medium is at room temperature, and the quenching time is 0.05 mm / min; the two-phase region cyclic quenching is repeated once; the forging after the two-phase region cyclic quenching is placed in a 200°C box furnace for holding for 1 hour for tempering, and naturally cooled after the tempering is completed to obtain a high-strength and high-toughness fibrous low-carbon alloy steel.

[0069] Example 3

[0070] The chemical composition of the high-strength and high-toughness fibrous low-carbon alloy steel in this embodiment is: C: 0.18%, Mn: 4.2%, Si: 0.93%, Cr: 0.8%, Mo: 0.33%, Nb+V≤0.1%, Al: 1.2%, and the remainder is Fe and unavoidable impurities.

[0071] The preparation method is as follows: the raw materials are melted and cast to obtain a billet with a size of 98 mm; the billet is heated to 1150°C and then forged in multiple passes with a total deformation rate of 79.59% and a final forging temperature of 850°C. After forging, it is slowly cooled to room temperature to obtain a forging.

[0072] The forging is austenitized in a 900°C vacuum tube furnace at a temperature of 1.5 mm / min, and then vertically placed in a quenching medium for quenching, wherein the quenching medium is salt water containing 5 wt% sodium chloride and 95 wt% water, the temperature of the quenching medium is room temperature, and the quenching time is 0.05 mm / min to obtain an austenitic forging. The austenitic forging is subjected to two-phase region cyclic quenching, specifically: first, the austenitic forging is placed in a tube furnace, kept at 840°C for 0.5 mm / min, and then quenched in salt water (5 wt% sodium chloride and 95 wt% water), when the temperature is higher than 300°C during the heating process, the heating rate is controlled at 5°C / min, and the quenching medium and related parameters are the same as those in Example 1; the number of two-phase region cyclic quenching is one; the forging after the two-phase region cyclic quenching is placed in a 200°C box furnace at a temperature of 1 hour for tempering, and naturally cooled after the tempering is completed to obtain a high-strength and high-toughness fibrous low-carbon alloy steel.

[0073] Example 4

[0074] The chemical composition of the high-strength and high-toughness fibrous low-carbon alloy steel in this embodiment is: C: 0.2%, Mn: 3.0%, Si: 0.88%, Cr: 0.8%, Mo: 0.32%, Nb+V≤0.1%, Cu: 0.95%, Al: 1.23%, and the remainder is Fe and unavoidable impurities.

[0075] The preparation method is as follows: the raw materials are melted and cast to obtain a billet with a size of 98 mm; the billet is heated to 1150°C and then subjected to multi-pass forging with a total deformation rate of 79.59% and a final forging temperature of 850°C. After forging is completed, it is slowly cooled to room temperature to obtain a forging.

[0076] The forging was austenitized in a vacuum tube furnace at a temperature of 1.5 mm / min, and then vertically placed in a quenching medium for quenching, wherein the quenching medium was salt water containing 5 wt% sodium chloride and 95 wt% water, the temperature of the quenching medium was room temperature, and the quenching time was 0.05 mm / min to obtain an austenitic forging. The austenitic forging was subjected to two-phase region cyclic quenching, specifically: first, the austenitic forging was placed in a tube furnace, kept at 820°C for 0.5 mm / min, and then quenched in salt water (5 wt% sodium chloride and 95 wt% water), when the temperature was higher than 300°C during the heating process, the heating rate was controlled at 3°C / min, and the quenching medium temperature and time were the same as those in Example 1; the number of two-phase region cyclic quenching was one; the forging after the two-phase region cyclic quenching was placed in a box furnace at a temperature of 200°C for 1 hour for tempering, and naturally cooled after the tempering was completed to obtain a high-strength and high-toughness fibrous low-carbon alloy steel.

[0077] Example 5

[0078] The chemical composition of the high-strength and high-toughness fibrous low-carbon alloy steel in this embodiment is: C: 0.2%, Mn: 3.0%, Si: 0.88%, Cr: 0.8%, Mo: 0.32%, Nb+V≤0.1%, Al: 1.31%, and the remainder is Fe and unavoidable impurities.

[0079] The preparation method is as follows: the raw materials are melted and cast to obtain a billet with a size of 98 mm; the billet is heated to 1150°C and then subjected to multi-pass forging with a total deformation rate of 79.59% and a final forging temperature of 850°C. After forging is completed, it is slowly cooled to room temperature to obtain a forging.

[0080] The forging was austenitized in a vacuum tube furnace at a temperature of 1.5 mm / min, and then vertically placed in a quenching medium for quenching, wherein the quenching medium was salt water containing 5 wt% sodium chloride and 95 wt% water, the temperature of the quenching medium was room temperature, and the quenching time was 0.05 mm / min, to obtain an austenitic forging. The austenitic forging was subjected to two-phase region cyclic quenching, specifically: first, the austenitic forging was placed in a tube furnace, and kept at 840°C for 0.5 mm / min. During the heating process, when the temperature was higher than 300°C, the heating rate was controlled at 8°C / min, and then quenched in salt water (5 wt% sodium chloride and 95 wt% water), the quenching medium temperature and time were the same as those in Example 1; the number of two-phase region cyclic quenching was one; the forging after the two-phase region cyclic quenching was placed in a box furnace at a temperature of 200°C for 1 hour for tempering, and naturally cooled after the tempering was completed to obtain a high-strength and high-toughness fibrous low-carbon alloy steel.

[0081] Performance testing:

[0082] (1) Morphology test

[0083] Figure 1 This is the SEM image of the high-strength and high-toughness fibrous low-carbon alloy steel prepared in Example 1. Figure 1 The organizational structure of fibrous martensite + ferrite can be seen, and there is also some residual austenite.

[0084] Figure 2 This is the EBSD image of the high-strength and high-toughness fibrous low-carbon alloy steel prepared in Example 1 (the scale is 20 μm). Figure 2 It can be seen that the slats are composed of a large number of fibers with consistent orientation.

[0085] Figure 3 TEM image of the high-strength and high-toughness fibrous low-carbon alloy steel prepared in Example 1. Figure 3 It can be seen that both martensite and ferrite have undergone bending deformation, showing good deformation coordination.

[0086] Figure 4This is the SEM image of the high-strength and high-toughness fibrous low-carbon alloy steel prepared in Example 2. Figure 4 It can be seen that the organizational morphology presents a fibrous structure of martensite + ferrite + retained austenite.

[0087] Figure 5 This is the SEM image of the high-strength and high-toughness fibrous low-carbon alloy steel prepared in Example 3. Figure 5 It can be seen that the organizational morphology presents a fibrous structure of martensite + ferrite + retained austenite.

[0088] Figure 6 This is the metallographic image of the high-strength and high-toughness fibrous low-carbon alloy steel prepared in Example 4. Figure 7 The metallographic diagram of the high-strength and high-toughness fibrous low-carbon alloy steel prepared in Example 5 is shown in FIG. Figures 6-7 It can be seen that the organizational morphology presents a fibrous structure of martensite + ferrite + retained austenite.

[0089] (2) Mechanical properties test

[0090] Figures 8 to 12 The engineering stress-strain curves of the high-strength and high-toughness fibrous low-carbon alloy steel prepared in Examples 1 to 5 are as follows; Figures 8 to 12 It can be seen that the tensile strength of the high-strength and high-toughness fibrous low-carbon alloy steels prepared in Examples 1 to 5 are all above 1300 MPa, and the elongation is all above 15%, among which the elongation of the low-carbon alloy steel in Example 2 reaches above 25%.

[0091] Figure 13 The engineering stress-strain curve of Example 1 after cold drawing is shown; Figure 13 It can be seen that the high-strength and high-toughness fibrous low-carbon alloy steel prepared in Example 1 is drawn from Φ14mm to Φ7mm through the cold drawing process, and its tensile strength reaches more than 2000MPa.

[0092] The hardness of the low carbon alloy steels obtained in Examples 1 to 5 was tested. The results showed that the hardness of Example 1 was 418.7 HV, the hardness of Example 2 was 431.3 HV, the hardness of Example 3 was 419.6 HV, the hardness of Example 4 was 410.9 HV, and the hardness of Example 5 was 442.4 HV.

[0093] In summary, the high strength and high toughness fibrous low carbon alloy steel provided by the present invention has the following properties: tensile strength R m ≥1300MPa, elongation A≥15%, hardness≥410HV.

[0094] The low-carbon steel material provided by the present invention is a high-performance material with high strength and toughness. It can be used in conjunction with other common steel materials, improving the overall performance of mechanical components while significantly reducing costs. Furthermore, the present invention utilizes a saltwater quenching medium, which significantly impacts environmental protection and is particularly suitable for practical industrial applications in bridge cable and wire. The addition of nickel, aluminum, and copper elements, through their associated alloying effects, not only optimizes the alloy's structure but also significantly improves its microstructure, strength, and plasticity, resulting in the material possessing exceptional mechanical properties.

[0095] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A high-strength and high-toughness fibrous low-carbon alloy steel, characterized in that: The invention comprises the following chemical components by mass fraction: C: 0.1-0.3%, Mn: 2-5%, Si: 0.3-1.5%, Cr: 0.3-1%, Mo: 0.1-0.8%, the total amount of Nb and V is ≤0.1%, Ni: 0-1.5%, Cu: 0-1.2%, Al: 0-1.5%, and the balance is Fe and unavoidable impurities; the contents of Ni, Al and Cu are not all 0 at the same time; the metallographic structure of the high-strength, high-toughness, low-carbon fiber-like alloy steel is a complex phase fibrous structure of martensite, ferrite and retained austenite.

2. The high-strength, high-toughness, low-carbon alloy steel according to claim 1, characterized in that: The high-strength and high-toughness low-carbon alloy steel has a tensile strength of ≥1300 MPa, an elongation of ≥15%, and a hardness of ≥410 HV.

3. The method for preparing the high-strength and high-toughness low-carbon alloy steel according to claim 1 or 2, characterized in that: The following steps are involved: (1) melting the raw materials and then casting to obtain a casting billet; (2) cooling the forged billet to obtain a forging; (3) austenitizing the forging and then quenching it to obtain an austenitic forging; (4) The austenitic forging is subjected to two-phase region cyclic quenching and then tempered to obtain the high-strength and high-toughness fibrous low-carbon alloy steel; the two-phase region cyclic quenching includes cyclic two-phase region heating and quenching; the temperature of the two-phase region heating is 700-840°C; the number of two-phase region cyclic quenching is greater than or equal to 1 time.

4. The preparation method according to claim 3, characterized in that The smelting temperature is 1400-1500° C., the casting temperature is 1400-1500° C.; the initial forging temperature is 1100-1200° C., the final forging temperature is 850-950° C.; the total deformation rate of the forging is 79-80%.

5. The preparation method according to claim 3, characterized in that The temperature of the austenitizing treatment is 890-910° C., and the holding time coefficient is 1.4-1.6 mm / min.

6. The preparation method according to claim 3, characterized in that The medium used for quenching in step (3) is brine, and the components of the brine include sodium chloride and water. The mass fraction of sodium chloride in the brine is 4-6%, and the mass fraction of water is 94-96%.

7. The preparation method according to claim 3, characterized in that The holding time coefficient of a single heating in the two-phase zone heating is 0.45 to 0.75 mm / min; During the process of heating to the temperature of the two-phase region heating, when the temperature is higher than 300° C., the heating rate is controlled at 2° C. / min to 15° C. / min.

8. The preparation method according to claim 3, characterized in that In the two-phase region circulating quenching, the quenching medium is brine, the components of the brine include sodium chloride and water, the mass fraction of sodium chloride in the brine is 4-6%, and the mass fraction of water is 94-96%.

9. The preparation method according to claim 3, characterized in that The tempering temperature is 150-200° C., and the tempering time is 50-70 minutes.

10. Use of the high-strength and high-toughness fibrous low-carbon alloy steel according to claim 1 or 2 or the high-strength and high-toughness fibrous low-carbon alloy steel prepared by the preparation method according to any one of claims 3 to 9 in the field of cable wire rod materials or machinery.

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